Percussion drill



June 18, 1963 E. L. COOK PERCUSSION DRILL Filed July 31, 1959 FIG. 6;

EVIN L. COOK INVENTOR FIG. I.

ATTORNEY United States Patent Office Patented June 18, 1963 3,094,176PERCUSSION DRILL Evin L. Cook, Dallas, Tex., assignor to Socony MobilOil Company, Inc., a corporation of New York Filed July 31, 1959, Ser.No. 830,778 13 Claims. (Cl. 175-92) This invention relates to drillingdevices and relates more particularly to fluid-actuated percussion-typedrilling devices.

Rotary-type drilling devices have long been extensively employed in thedrilling of oil wells. To a much lesser extent percussion-type drillingdevices have been used in well drilling. Some percussion devices havebeen combined with rotary devices to provide improved means for drillingin particularly hard rock formations.

Drilling devices which utilize the principle of percussive action werefirst suggested many years ago. Through the years devices have beenproposed which achieve percussive action in numerous different ways.Among the suggested ways of obtaining percussive action in drilling havebeen devices which employ the water hammer effect obtained by a suddeninterruption of the flow of a fluid. One of the early drilling toolswhich was proposed to operate by the water hammer eflect is disclosed inUS. Patent No. 699,27 3 issued to W. Wolski on May 6, 1902. In recentyears there have been few developments relating to this type of drillingapparatus.

In those instances where percussion type drilling devices have beencombined with rotary drilling devices, the water hammer effect has beenobtained by sudden interruption of the flow of drilling fluids, oftencalled drilling muds, which are normally used to cool the bit, flushcuttings from the well, and maintain a hydrostatic pressure on thefluids and gases in the formation surrounding the well. This suddeninterruption of fluid flow referred to above has generally been acomplete stoppage of all fluid flow. Sudden and complete stoppage of theflow of a drilling fluid results in at least two eflfects which may bedetrimental. First, it causes the transmission of shock waves up thedrill string with a resultant loss of energy and also mechanicalvibration which can be damaging to drilling equipment, such as, pumps,the rotary table, etc., used on the surface. Second, completeinterruption of drilling fluid flow may reduce the eifectiveness of theflushing action of the fluid.

In the past, the problem of protection of equipment from the effects ofa water hammer has been recognized and to some extent shock has beenminimized by the use of an enlarged section in the drill string betweenthe bit and the pumps. This enlarged section has been proposed both tocontrol the frequency of the impacts caused by the water hammer and alsoto provide a cushion to absorb some of the impact to prevent itsreaching the pumps and other equipment used. In none of the known liquiddriven percussion-type devices which employ the water hammer effect todrive the bit has there been any means for providing continuous flushingof cuttings or permitting continued rotary drilling in event of failureof the percussion device. Failures of the percussion devices by way ofvalves sticking or otherwise showing faulty operation have requiredcomplete shutting down of the drilling operation.

Some of the more recently developed percussion type drilling deviceshave employed massive hammers which in part are actuated by drillingfluid. The present invention achieves its driving force not from themass of a hammer device but rather from the mass and velocity of acolumn of drilling fluid.

Several advantages inherent in the present invention are as follows.Transmission of mechanical vibration to surface drilling equipment isminimized. The mass of a column of drilling fluid provides the drivingforce for the percussive cutting action of the device. Thoughconventional rotary bits may be used with the device, it is alsopossible to use solid head chisel type :bits which are not subject tosuch weaknesses of the rotary bit as bearing failures. The device of thepresent invention also permits continuous drilling fluid flushing actionsince it is never necessary that the entire flow of drilling fluid bestopped to obtain percussive action of the bit.

It is an object of the present invention to provide a fluid-actuatedpercussion-type drilling apparatus which may be employed in conjunctionwith rotary type drilling apparatus. It is another object of theinvention to provide a percussion-type drilling apparatus in which it isnot necessary to completely interrupt the flow of all drilling fluidpassing through the bit. It is another object of the invention toprovide percussion drilling apparatus which minimizes the transmissionof shock waves up the drill string to surface equipment. It is anotherobject of the invention to provide percussion drilling apparatus whichpermits continuous flushing of cuttings from the well. It is a furtherobject of the invention to provide combination rotary and percussiondrilling apparatus which will permit continued rotary drilling whenvalve failures occur in the percussion drilling apparatus. It is anotherobject of the invention to provide a drilling device which may be usedwith a variety of types of bits. These and additional objects of theinvention will be evident from a reading of the following specificationand drawings.

Referring to the drawings:

FIG. 1 is a longitudinal cross-sectional View illustrating one form ofpercussion drilling apparatus constructed in accordance with theinvention;

FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1;

FIG. 3 is a view in cross section taken along the line 3-3 of FIG. 1;

FIG. 4 is a cross-sectional view taken along the line 4-4 of FIG. 1;

FIG. 5 is a view in cross section taken along the line 5-5 of FIG. 1;and

FIG. 6 is a longitudinal, cross-sectional view of the lower portion of amodified form of the percussion drilling apparatus shown in FIG. 1.

Referring to FIGS. 1-5, outer tube 10 is a special section of pipe ordrill collar secured to the lower end of a drill string, not shown, andis adapted to support percussion drilling apparatus which is operablesimultaneously with rotary drilling. The drill string to which tube 10is secured extends from a rotary table at the surface and functions torotate the percussion apparatus and convey drilling fluid to it. At itslower end, tube 10 is provided with a plurality of internal longitudinalkeyways 12 in the form of slots which are cut into the inside surface ofthe tube and extend into the tube a predetermined distance from the endof the tube. Threaded onto the lower end of tube 10 is a tubular closuremember 13 which has the same inner and outer diameters as tube 10.Closure member 13 provides a shoulder 13a at the lower ends of each ofkeyways 12.

Positioned within the lower portion of tube 10 is a tubular-shaped valvebody and connecting member 20 which is provided at its upper end with aportion of reduced diameter 21. The upper end of portion 21 of body 20is provided with a longitudinal valve chamber 22 which is cylindrical inform, is closed at its lower end, and is open at its upper end. Thelongitudinal axis of valve chamber 22 is positioned coincident with thelongitudinal axis of body member 20. Portion 21 of member 20 is providedwith a plurality of radial flow passages 23 which slope downwardly andoutwardly from chamber 22 and serve to provide fluid communicationthrough the wall of the chamber from a position intermediate the ends ofthe chamber. A valve 24 is positioned within chamber 22 to provide amoveable closure for the upper open end of the chamber. The stem ofvalve 24 extends through chamber 22, terminating near the lower closedend of the chamber and is connected to a spring 25 which is secured inthe lower closed portion of the chamber and serves to urge the valveupwardly into an open position. Portion 21 of member 20 is provided witha small tubular passageway 26 which extends into the bottom of chamber22 to permit fluid to flow into and out of the chamber as the valve stemchanges position in the chamber. This is desirable to control the effectof the fluid upon valve action with changes in valve position. Thediameter of passage 26 may be varied in order to obtain the desiredmodulated valve action.

Body member 20 is provided with an axial flow passage 30 which connectswith a plurality of radially-positioned flow passages 31 which slopedownwardly and inwardly to connect with the upper end of flow passage30. It is not necessary that the exact configuration of passages 30 and31 be adhered to so long as their function is provided by passage meansthrough member 20 to permit constant fluid flow from tube through memberinto the bit. Formed along the outer surface of body member 20 are aplurality of external splines or longitudinal keys 40 which are equal innumber to keyways 12 and so positioned that they will mesh with keyways12 to permit body member 20 to be rotated by tube 10. Keyways 12 arelonger than keys 40 in order that body member 20 may slidelongitudinally within tube 10. Upward movement of body member 20 islimited by the upper ends of keyways 12, while downward movement of bodymember 20 is limited by member 13 which forms the closure for the lowerends of keyways 12. In cross section, keys 40 and keyways 12 are sosized that there is a slip fit between them which will permit thislongitudinal movement.

Bit adapter 50 is threaded into the lower end of member 20 and isprovided with a flow passage 51 which registers with flow passage 30 inmember 20. Adapter 50 is provided with a shoulder 52 which abuts againstthe lower end of member 13 when tube 10 is urged in a downwarddirection. Threaded into the lower end of bit adapter 50 is a drill bit55 which is provided with a central flow passage 56 and a plurality ofradial flow passages 57. Bit adapter 50 functions to secure the bit tothe drilling apparatus and to conduct drilling fluid from passage 30 inmember 20 into the flow passages 56 and 57 of the bit.

Positioned within tube 10 and secured to and supported by member 20 isan inner tube 60. The lower end of tube 60 is secured to the upper endof portion 21 of member 20 by means of threads or any other suitableconnecting means. The longitudinal axis of inner tube 60 lies coincidentwith the longitudinal axis of tube 10. The length of tube 60 isdetermined by considerations which include the frequency of impactsdesired to be obtained by the percussion apparatus, as will be explainedhereinafter. The internal bore of tube 60 provides a central fluid flowpassage 61, while the external surface of tube 60 and the internalsurface of tube 10 define an annular fluid flow passage 62. A pluralityof guides 70 and 71 are rigidly secured around the outside of inner tube60 to maintain the tube in its proper position within tube 10. Guides 70and 71 are not secured to the inner surface of tube 10' but rather areof such length that there will be a slip fit between the guides and theinner surf-ace of tube 10 to permit longitudinal motion of tube 60'relative to tube 10. The particular placement of the guides and thenumber of guides employed are dependent upon the length and rigidity oftube 60. It is necessary to use only the number of guides required topermit the maintenance of tube 60 in its proper position. As may beobserved in FIG. 2, the size of the guides should be such that they willprovide a minimum amount of interference with the desired fluid flowthrough annulus 62.

It will be recognized from the above description that the assemblycomprising inner tube 60, body member 20 with its associated valve 24,bit adapter 50, and bit 55 form a unit which is free to movelongitudinally within defined limits in tube 10 and is rotated with andby tube 10.

Referring to FIG. 6, the percussion drilling apparatus illustrateddiffers from the embodiment shown in FIG. 1 in the provision of a bitadapter 80 which is of substantial length. Due to the substantial lengthof bit adapter 80, it is necessary that it :be constructed such that itsresonant frequency is equal to the frequency of the impacts delivered bythe percussion apparatus with which it is employed. For example, bitadapter 80 may be as long as 100 feet or more. It will readily berecognized that such a lengthy member will have such a large mass andconsequently a resonant frequency which must be correlated with thefrequency at which the tool is to function in order to prevent the bitadapter from vibrating at cross purposes or in opposition to the impactforces developed by the tool. In other words, if the resonant frequencyof such a massive element is not correlated with the frequency for whichthe tool is designed, the bit adapter may start vibrating out of unisonwith the tool impact frequency and thus not effectively transmit theimpacts from the tool to the bit. The bit adapter may be designed inaccordance with the following formula:

where:

f=the frequency at which the tool is designed to operate,

c==the velocity of sound in the material from which the bit adapter isconstructed, and

l=the length of the bit adapter.

Operation of the percussion drilling apparatus is effected by employmentof drilling fluid normally used in rotary drilling to produce percussiveaction concurrent with rotary drilling action. Drilling fluid is pumpeddownwardly through the drill string into tube 10 until it arrives at theupper end of inner tube 60 at which point the drilling fluid is dividedby tube 60 into two streams of flow. One stream of flow passes withintube 60 through central passage 61, while the other stream of drillingfluid passes downwardly through annular flow passage 62. The stream offluid flowing through passage 61 passes around valve 24 which is beingheld in an open position by spring 25, through chamber 22, and outwardlyfrom the chamber through passages 23 into annulus 62 where it rejoinsthe fluid flowing in annulus 62. The combined streams of drilling fluidthen flow into body 20 through passages 31, through passages 30 and 51,into and outwardly from the bit into contact with the format-ion beingX=the distance which the spring must be displaced to effect valveclosure.

The forces operating on the valve at the instant before closure arerepresented by the following formula:

where K=the spring constant;

X=the distance which the spring must be displaced to effect valveclosure;

AP the pressure loss through the valve opening; and

A=the etfective area of the valve.

It will be recognized from the above formula and the definitions of itsterms that prior to valve closure the force holding the valve open isthat which is being exerted by the spring. This force is, of course,that which must be overcome in order for the flowing fluid to eifectclosure of the valve. It can thus [be seen that at the momentimmediately prior to the liquid forcing the valve closed the force beingexerted by the pressure drop across the valve as represented by AP Awill be equal to the force KX which is holding the valve open. At themoment that AP A exceeds the force holding the valve open, the valvewill abruptly close.

The period of operation of the valve mechanism itself,-

that is, the time required for the valve to move from open to closedposition and vice versa, is controlled by the weight and design of valveused, the spring member, and other considerations such as the viscosityof the fluid. The natural frequency of the valve mechanism should beequal to or greater than the frequency of the impacts to be delivered bythe percussion drilling apparatus in order that the natural or resonantfrequency of the valve will not interfere with the timing of the impactsof the percussion drilling apparatus. In other words, for satisfactoryvalve operation the valve should be of such design that it can completeits movements in less time than the period between impacts which isestablished by the length of inner tube 60. A formula which may beemployed in the design of the valve mechanism is as follows:

;f=the frequency in cycles per second at which the tool is to operate;

C=the velocity of sound in the drilling fluid employed to actuate thetool;

l=the length of the central flow passage 61 within inner tube 60;

K=the spring constant of spring 25;

g=the gravitational constant; and

W=the weight of valve 24 and spring 25.

The abrupt closure of the valve creates a water hammer effect, which isan abrupt pressure build-up, that acts as a driving force on bit 55effected by downward dis placement of the assembly comprising inner tube60, body 20, and adapter 50. The magnitude of the force exerted on thebit is expressed in the formula:

: ApCAV where:

where f=the frequency in cycles per second;

c=the velocity of sound in the drilling fluid; and

l=the length of the central flow passage 61 within inner tube 60.

Since the frequency and the length of the flow passage 61 areinterdependentvariables, it will be readily recognized that thefrequency desired may be obtained by constructing the tube 60 with thelength necessary to satisfy the above formula. Though the frequency ofthe impacts delivered by the percussion device is not dependent upon thevalve 24 employed or the period of operation of the valve, it isnecessary, as has been previously pointed out, that due consideration begiven this frequency in designing the valve in order that the period ofoperation of the valve will be greater than the frequency so that thevalve may go through its complete cycle of operation between impacts.

Upon closure of valve 24, the sudden stoppage of flow within passage 61initiates a compression wave in the drilling fluid at the valve."Simultaneously with the initiation of the compression wave at thevalve, a rarefaction wave is formed in the drilling fluid immediatelybelow the valve. The compression wave travels upwardly in passage 61,while the rarefaction wave moves through chamber 22 and passages 23 intoannulus 62 where it travels both upwardly and downwardly within theannulus. The portion of the rarefaction Wave moving downwardly in theannulus passes through passages 31, 30, and 51 through the bit toproduce a lower pressure upon the formation being drilled. The impactcaused by the compression Wave at valve 24 acts through body member 20and adapter 50 to force the bit into the formation at substantially thesame time that the rarefaction wave reaches the formation. The reducedpressure created by the rarefaction wave improves the cutting action ofthe bit.

The compression wave moving upwardly in passage 61 and that portion ofthe rarefaction wave moving upwardly in annulus 62 both arrive at thetop of tube 60 at approximately the same time. Since the cross-sectionalarea of the interior of tube 10 is larger than either passage 61 orannulus 62, the area within tube 10 above tube 60 will, in accordancewith well-known principles of fluid mechanics, act as a reflector forboth the compression wave in passage 61 and the rarefaction wave inannulus 62. At the top of tube 60 a part of the compression wave movingupwardly in passage 61 is substantially reflected, that is, thereflected compression wave becomes a rarefaction wave which passesdownwardly through passage 61 to valve 24. At the same time, therarefaction wave in annulus 62 is partially reflected at the top of tube60, that is, the reflected rarefaction wave becomes a compression waveand passes downwardly through the annulus and into chamber 22 throughpassage 23. The reflected waves arrive at the zone around valve 24 atsubstantially the same time. The top of the valve is under the influenceof a rarefaction wave and the bottom of the valve is under the influenceof a com pression wave, causing the valve, with the assistance of spring25, to move to a full, open position. With the valve open, the fluidwithin passage 61 again accelerates to the velocity necessary to closethe valve and thus repeat the cycle.

As it has been stated that the compression wave created upon closure ofthe valve moves upwardly in pas sage 61 and is partially reflected atthe top of tube 60, it will be recognized that the interface at the endof the tube acts as a reflector and thus a portion of this compressionwave not reflected will tend to move upwardly through tube 10 to theequipment on the surface. Similarly, the interface at the end of tube 60acts as a reflector to rarefaction waves rising through the annulus 62.The term interface as used herein means a widening in the path ofmovement of the waves, compression and rarefaction, which results in areflection or change in character of the waves. For example, acompression wave arriving at the top of tube 60 spreads out into tube1-0 and begins diminishing and changing into a rarefaction wave. Thesimultaneous arrival of a rarefaction wave at the top of tube 60 withinannulus 62 will tend to reduce and possibly cancel the portion of thecompression wave which is being transmitted upwardly within tube 60. Byemployment of recognized principles of fluid mechanics it is possible toadjust the internal diameters of tubes 10 and 60 such that therelationship between the crosssectional areas of passage 61 and annulus62 will be so related that the compression wave moving upwardly inpassage 61 will be completely canceled by the rarefaction wave movingupwardly in annulus 62 with the result that no shock is transmitted upto the surface equipment. The provision of an inner tube 60 ofsufficient size to deliver a maximum impulse to the bit is, however, notnecessarily compatible with the complete elimination of transmission ofshock upwardly through tube 10 to the surface equipment. While increasesin the force of the impact deliverable by the apparatus are directlyrelated to increases in the cross-sectional area of passage 61,decreases in the amount of shock delivered upwardly through tube 10 arerelated to minimizing the cross-sectional area of passage 61 relative tothe crosssectional area of annulus 62. It is desirable, therefore, inorder to obtain a maximum impact upon the bit that the apparatus bedesigned with tube sizes which will permit transmission of shockupwardly through tube 10 within limits which may be tolerated by thesurface equipment.

As has been previously stated, percussion drilling apparatus constructedin accordance with the invention permits continuous flow of drillingfluids to the formation at the same time that percussive impacts arebeing delivered to the bit. The drilling fluid flowing through annulus62 is never completely stopped during the operation of the apparatus.Should the valve 24 become inoperable, rotary drilling may be continuedwithout removing the apparatus from the well bore because of the factthat the flow of drilling fluid continues through annulus 62.

The manner of operation and advantages discussed above are equallyapplicable to the modified form of the invention disclosed in FIG. 6.While the bit adapter shown in FIG. 1 is sufliciently short in lengthand low in mass that the frequency of operation of the device is notsignificant in the design of the adapter, it is necessary to considersuch frequency with respect to bit adapter 80'. The length of bitadapter 80 should be such that its resonant frequency equals thefrequency of the interruptions in the flow of the drilling fluid. Therelationships of the factors involved are expressed in the formula:

where:

f=frequency in cycles per second;

c=velocity of sound in the drilling fluid;

l=length of the central flow passage 61 within inner tube 60;

c' =velocity of sound in bit adapter; and

l'=length of bit adapter.

Bit adapter 80 may, as a practical matter, be constructed from one ormore lengths of conventional drill collar.

While the invention has been described in the light of certain specificembodiments, it will be recognized that other modifications will occurto those skilled in the art and it is intended that the invention willbe limited only within the scope of the appended claims.

I claim:

1. In a fluid actuated percussion drilling device the combination whichcomprises an outer tube, an inner tube concentrically positioned withinand spaced apart from said outer tube, said inner tube being open at theupper end thereof into said outer tube, a valve at the lower end of saidinner tube, spring means on said valve for holding said valve open untilfluid flow through said inner tube exceeds a predetermined rate, andbody means slidably secured within said outer tube for supporting saidinner tube and valve, said body means being provided with at least onefluid flow passage therethrough in communication with the lower end ofsaid inner tube to permit fluid to flow from said inner tube into saidouter tube and at least one fluid flow passage therethrough incommunication with said outer tube and extending downwardly through thelower end of said body means, said inner tube, valve, and body meanscomprising an assembly adapted to reciprocate in response tointerruptions etfected in fluid flow through said inner tube by actionof said valve.

2. In a fluid-actuated percussion drilling device the combination whichcomprises an outer tube, an inner tube concentrically positioned withinand spaced apart from. said outer tube, said inner tube being open atthe upper end thereof into said outer tube, a valve in the lower end ofsaid inner tube operable in response to fluid flow through said innertube, spring means on said valve for holding said valve open until fluidflow through said inner tube exceeds a predetermined rate, and bodymeans slidably secured within said outer tube for supporting said innertube and valve, said body means being provided with passages fordirecting fluid flow from the lower end of said inner tube into saidouter tube and passages for directing fluid flow from said outer tubedownwardly through said body means, said inner tube, valve, and bodymeans comprising an assembly adapted to reciprocate in response tointerruptions effected in fluid flow through said inner tube by actionof said valve.

3. In a fluid-actuated percussion drilling device the combination whichcomprises an outer tube, an inner tube concentrically positioned withinand spaced apart from said outer tube to provide a central fluid flowpath and an annular fluid flow path, the upper end of said inner tubebeing open into said outer tube, body means secured to the lower end ofsaid inner tube, said body means being slidably secured within saidouter tube, said body means being provided in the upper portion thereofwith a valve chamber opening into said inner tube and fluid flowpassages leading from said valve chamber to permit fluid flow from thelower end of said inner tube into said annular flow path, said bodymeans being further provided with a lower central flow passage and aplurality of connecting flow passages to permit fluid flow from saidannular flow path downwardly through said body means, a valve supportedin said valve chamber at the lower end of said inner tube, and a springon said valve for holding said valve open until fluid flow through saidinner tube exceeds a predetermined rate, said inner tube, valve, andbody means comprising an assembly adapted to reciprocate relative tosaid outer tube in response to interruptions in fluid flow through saidinner tube etfected by operation of said valve.

4. In a fluid-actuated percussion drilling device the combination whichcomprises an outer tube provided in the lower portion thereof with aplurality of radiallyspaced, internal, longitudinal keyways, a collarthreaded to the lower end of said outer tube to provide a closure forthe lower ends of said keyways, a body member provided with an upperportion of reduced diameter positioned in the lower portion of saidouter tube, said body member being provided with a plurality oflongitudinal, external keys spaced to mesh with said keyways in saidouter tube, said keys and keyways being so related in cross section thatsaid body member may slide longitudinally in said outer tube While beingrotated by said outer tube, said body member being provided with a valvechamber at its upper end and a plurality of radial flow passagesextending outwardly from said valve chamber to permit fluid flowdownwardly into the upper end of said body member and outwardly intosaid outer tube, said body member being further provided with aplurality of radial flow passages at the lower end of said pornon ofreduced diameter, said radial flow passages being connected at theinward ends thereof with a central flow passage extending downwardlythrough the lower end of said body member, a bit connecting membersecured to the lower end of said body member, said bit connecting memberbeing provided with a shoulder for abutting against said collar to limitupward movement of said body member, an inner tube secured to the upperend of said body member and concentrically positioned within and spacedapart from said outer tube, said inner and outer tubes forming centraland annular fluid flow paths, said inner tube being open at the upperend thereof into said outer tube and at the lower end thereof into saidvalve chamber, means secured around said inner tube for maintaining saidinner tube in alignment with said outer tube and permitting said innertube to move longitudinally relative to said outer tube, a valvesupported in said valve chamber at the lower end of said inner tube, anda spring on said valve to hold said valve open until fluid flow throughsaid inner tube exceeds a predetermined rate, said valve being adaptedto close in response to a predetermined rate offluid flow through saidinner tube to efiect interruptions in said fluid flow, said fluid flowinterruptions effecting sudden downward movement of the assemblycomprising said inner tube, said body member, said valve, and said bitconnecting member.

5. In a fluid-actuated percussion drilling device the combination whichcomprises an outer tube, an inner tube concentrically positioned withinand spaced apart from said outer tube, said inner tube being open at theupper end thereof into said outer tube, a valve at the lower end of saidinner tube, said valve having a natural frequency of operation greaterthan the frequency of impacts deliverable by said device, the distancebetween said valve and the upper end of said inner tube being inaccordance with the formula:

where 1 equals the distance between said valve and the top of said innertube, c equals the velocity of sound in fluid flowing through saiddevice, and 1 equals the frequency of impacts deliverable by saiddevice, a spring on said valve to hold said valve open until fluid flowthrough said inner tube exceeds a predetermined rate, and body meanssecured to the lower end of said inner tube to support said inner tubeand valve and direct fluid flow from said inner tube and said outer tubedownwardly, said body means being provided with fluid flow passage meansto permit fluid flow from said inner tube around said valve into saidouter tube and fluid flow passage means to permit fluid flow from saidouter tube downwardly through the lower end of said body means, saidbody means being slidably secured within and rotatable by said outertube, said inner tube, valve, and body means comprising an assemblyadapted to reciprocate relative to said outer tube in response tointerruptions in fluid flow through said inner tube effected by actionof said valve.

'6. In a fluid-actuated percussion drilling device the combination whichcomprises an outer tube, an inner tube concentrically positioned withinand spaced apart from said outer tube to provide a central fluid flowpath and an annular fluid flow path, said inner tube being open at theupper end thereof into said outer tube, body means secured to the lowerend of said inner tube, said body means being slidably secured withinsaid outer tube, said body means being provided with a valve chamber atthe upper end thereof opening into said inner tube and fluid flowpassages leading from said valve chamber to permit fluid flow from thelower end of said inner tube through said valve chamber into saidannular flow path, said body means being further provided with a lowercentral flow passage and a plurality of connecting flow passages topermit fluid flow fnom said annular flo-w path downwardly through saidbody means, a valve supported in said valve chamber at the lower end ofsaid inner tube, and a spring on said valve to hold said valve openuntil fluid flow through said inner tube exceeds a predetermined rate,the relation between the frequency of impacts deliverable by said deviceand the distance between said valve and the upper end of said inner tubebeing in accordance with the formula:

where 1 equals the distance between said valve and the upper end of saidinner tube, 0 equals the velocity of sound in fluid flowing through saiddevice, and f equals the frequency of impacts deliverable by saiddevice, said inner tube, valve, and body means comprising an assemblyadapted to reciprocate relative to said outer tube in response tointerruptions in fluid flow through said inner tube eflected byoperation of said valve.

7. In a fluid-actuated percussion drilling device the combination whichcomprises an outer tube provided in the lower portion thereof with aplurality of radiallyspaced, internal, longitudinal keyways, a collarthreaded to the lower end of said outer tube to provide a closure forthe lower ends of said keyways, a body member provided with an upperportion of reduced diameter positioned in the lower portion of saidouter tube, said body member being provided with a plurality oflongitudinal, external keys spaced to mesh with said keyways in saidouter tube, said keys and keyways being so related in cross section thatsaid body member may slide longitudinally in said outer tube while beingrotated by said outer tube, said body member being provided with a valvechamber at its upper end and a plurality of radial flow passagesextending outwardly from said valve chamber to permit fluid flowdownwardly into the upper end of said body member and outwardly intosaid outer tube, said body member being further provided with aplurality of radial flow passages at the lower end of said portion ofreduced diameter, said passages being connected at the inward endsthereof with a central flow passage extending downwardly through thelower end of said body member, a bit connecting member secured to thelower end of said body member, said bit connecting member being providedwith a shoulder for abutting against said collar to limit upwardmovement of said body member, an inner tube secured to the upper end ofsaid body member and concentrically positioned within and spaced apartfrom said outer tube, said inner tube being open at the upper endthereof into said outer tube, said inner and outer tubes forming centraland annular fluid flow paths, means secured around said inner tube formaintaming said inner tube in alignment with said outer tube andpermitting said inner tube to move longitudinally relative to said outertube, a valve supported in said valve chamber at the lower end of saidinner tube, and a spring on said valve to hold said valve open untilfluid flow through said inner tube exceeds a predetermined rate, therelation between the frequency of impacts deliverable by said device andthe distance between said valve and the upper end of said inner tubebeing in accordance with the formula:

where l equals the distance between said valve and the upper end of saidinner tube, 0 equals the velocity of sound in fluid flowing through saiddevice, and 1 equals the frequency of impacts deliverable by saiddevice, said valve being adapted to close in response .to apredetermined rate of fluid flow through said inner tube to eflectinterruptlons in said fluid flow, said fluid flow interruptionseffecting sudden downward movement of the assembly comprising said innertube, said body member, said valve, and said bit connecting member.

8. In a fluid-actuated percussion drilling device the combination whichcomprises an outer tube, an inner tube concentrically positioned withinand spaced apart from said outer tube, said inner tube being open at theupper end thereof into said outer tube, a valve at the lower end of saidinner tube, a spring on said valve to hold said valve open until fluidflow through said inner tube exceeds a predetermined rate, body meansslidably secured within said outer tube for supporting said inner tubeand valve said body means being provided with fluid flow passages forconducting fluid from the lower end of said inner tube around said valveinto said outer tube and fluid flow passages for conducting fluids fromsaid outer tube downwardly through the lower end of said body means andan elongated, tubular-shaped bit connecting member secured to the lowerend of said body means for securing a bit and conducting fluid flow fromsaid body means to said bit, said bit connecting member having aresonant frequency equivalent to the frequency of impacts deliverable bysaid device, said inner tube, said body means, said valve, and said bitconnecting member comprising an assembly adapted to reciprocate relativeto said outer tube in response to interruptions in fluid flow throughsaid inner tube effected by operation of said valve.

9. In a fluid-actuated percussion drilling device the combination whichcomprises an outer tube, an inner tube concentrically positioned withinand spaced apart from said outer tube to provide a central fluid flowpath and an annular fluid flow path, said inner tube being open at theupper end thereof into said outer tube, body means secured to the lowerend of said inner tube and slidably secured within said outer tube, saidbody means being provided with a valve chamber at the upper end thereofand fluid flow passages leading from said valve chamber to permit fluidflow from the lower end of said inner tube into said annular flow path,said body means being further provided with a lower central flow passageand a plurality of connecting flow passages to permit fluid flow fromsaid annular flow path downwardly through said body means, a valvesupported in said valve chamber at the lower end of said inner tube, aspring secured to said valve for holding said valve open until fluidflow through said inner tube exceeds a predetermined rate, and atubular-shaped bit connecting member secured to the lower end of saidbody means for securing a bit to and conducting fluid from said bodymeans to said bit, said bit connecting member having a resonantfrequency equivalent to the frequency of impacts deliverable by saiddevice, said inner tube, body means, valve, and bit connecting membercomprising an assembly adapted to reciprocate relative to said outertube in response to to interruptions in fluid flow through said innertube effected by operation of said valve.

10. 'In a fluid-actuated percussion drilling device the combinationwhich comprises an outer tube provided in the lower portion thereof witha plurality of radiallyspaced, internal, longitudinal keyways, a collarthreaded to the lower end of said outer tube to provide a closure forthe lower ends of said keyways, a body member provided with an upperportion of reduced diameter positioned in the lower portion of saidouter tube, said body member being provided with a plurality oflongitudinal, external keys spaced to mesh with said keyways in saidouter tube, said keys and keyways being so related in cross section thatsaid body member may slide longitudinally in said outer tube while beingrotated by said outer tube, said body member being provided with a valvechamber at its upper end and a plurality of radial flow passagesextending outwardly from said valve chamber to permit fluid flowdownwardly into the upper end of said body member and outwardly intosaid outer tube, an inner tube concentrically positioned within saidouter tube and secured at the lower end thereof to said body member, theupper end of said inner tube being open into said outer tube, a valvesecured in said valve chamber to control the flow of fluid through saidinner tube, a spring secured to said valve to hold said valve open untilfluid flow through said inner tube exceeds a predetermined rate, saidbody member being further provided with a plurality of radial flowpassages at the lower end of said portion of reduced diameter, saidradial flow passages being connected at the inward ends thereof with acentral flow passage extending downwardly through the lower end of saidbody member, and an elongated, tubular-shaped bit connecting membersecured to the lower end of said body member for securing a bit andconducting fluid flow from said body member to said bit, said bitconnecting member having a resonant frequency equal to the frequency ofimpacts deliverable by said device.

11. In a fluid-actuated percussion drilling device the combination whichcomprises an outer tube, an inner tube concentrically positioned withinand spaced apart from said outer tube, the upper end of said inner tubebeing open into said outer tube, a valve at the lower end of said innertube, a spring on said valve to hold said valve open until fluid flowthrough said inner tube exceeds a predetermined rate, said valve havinga natural frequency of operation greater than the frequency of impactsdeliverable by said device, the distance between said valve and theupper end of said inner tube being in accordance with the formula where1 equals the distance between said valve and the top of said inner tube,0 equals the velocity of sound in fluid flowing through said device, andf equals the frequency of impacts deliverable by said device, a bodymember secured to the lower end of said inner tube to support said innertube and valve and direct fluid flow from said inner tube and said outertube downwardly, said body member being slidably secured within androtatable by said outer tube, said body member being provided with fluidflow passages for conducting fluid from the lower end of said inner tubethrough said body member into said outer tube and fluid flow passagesfor conducting fluids from said outer tube downwardly and outwardlythrough the lower end of said body member, and an elongated,tubularshaped bit connecting member secured to the lower end of saidbody member for securing a bit and conducting fluid flow from said bodymember to said bit, the length of said bit connecting member being inaccordance with the formula:

where 1' equals the length of said bit connecting member, c equals thevelocity of sound in said bit connecting member, and f equals thefrequency of impacts deliverable by said device, said inner tube, bodymember, valve, and bit connecting member comprising an assembly adaptedto reciprocate relative to said outer tube in response to interruptionsin fluid flow through said inner tube effected by operation of saidvalve.

12. In a fluid-actuated percussion drilling device the combination whichcomprises an outer tube, an inner tube concentrically positioned withinand spaced apart from said outer tube to provide a central fluid fiowpath and an annular fluid flow path, the upper end of said inner tube'being open into said outer tube, a body member secured to the lower endof said inner tube and slidably secured within said outer tube, saidbody member being provided with a valve chamber at the upper end thereofand fluid flow passages leading from said valve chamber to permit fluidflow from the lower end of said inner tube into said annular flow path,said body member being further provided with a lower central flowpassage and a plurality of connecting flow passages to permit fluid flowfrom said annular flow path downwardly through said body member, and avalve supported in said valve chamber at the lower end of said innertube, a spring on said valve to hold said valve open until fluid flowthrough said inner tube and valve chamber exceeds a predetermined rate,the distance between said valve and the upper end of said inner tubebeing in accordance with the formula:

where 1 equals the distance between said valve and the top of said innertube, 0 equals the velocity of sound in fluid flowing through saiddevice, and f equals the frequency of impacts deliverable by saiddevice, and a tubular-shaped bit connecting member secured to the lowerend of said body member for securing a bit and conducting fluid flowfrom said body member to a bit, the length of said bit connecting memberbeing in accordance with the formula:

f where l' equals the length of said bit connecting member, c equals thevelocity of sound through said bit connecting member, and 1 equals thefrequency of impacts deliverable by said device, said inner tube, valve,and body means comprising an assembly adapted to reciprocate relative tosaid outer tube in response to interruption in fluid flow through saidinner tube effected by operation of said valve.

13. In a fluid-actuated percussion drilling device the combination whichcomprises an outer tube provided in the lower portion thereof with aplurality of radiallyspaced, internal, longitudinal keyways, a collarthreaded to the lower end of said outer tube to provide a closure forthe lower ends of said keyways, a body member provided with an upperportion of reduced diameter positioned in the lower portion of saidouter tube, said body member being provided with a plurality oflongitudinal, external keys spaced to mesh with said keyways in saidouter tube, said keys and keyways being so related in cross section thatsaid body member may slide longitudinally in said outer tube while beingrotated by said outer tube, said body member being provided with a valvechamber at its upper end and a plurality of radial flow passagesextending outwardly from said valve chamber to permit fluid flowdownwardly into the upper end of said body member and outwardly intosaid outer tube, said body member being further provided with aplurality of radial flow passages at the lower end of said portion ofreduced diameter, said radial flow passages being connected at theinward ends thereof with a central flow passage extending downwardlythrough the lower end of said body member, a tubular-shaped bitconnecting member secured to the lower end of said body member forsecuring a bit and conducting fluid flow from said body member to saidbit, the

length of said bit connecting member being in accordance with theformula:

where 1' equals the length of said bit connecting member, 0 equals thevelocity of sound through said bit connecting member, and 1 equals thefrequency of impacts deliverable by said device, said bit connectingmember being provided with a shoulder for abutting against said collarto limit upward movement of said body member, an inner tube secured tothe upper end of said body member and concentrically positioned withinand spaced apart from said outer tube, the upper end of said inner tubebeing open into said outer tube, said inner and outer tubes formingcentral and annular fluid fiow paths through said device, means securedaround said inner tube for maintaining said inner tube in alignmentwithin said outer tube and permitting said inner tube to movelongitudinally relative to said outer tube, a valve supported in saidvalve chamber at the lower end of said inner tube, the distance betweensaid valve and the upper end of said inner tube being in accordance withthe formula:

where l equals the distance between said valve and the top of said innertube, c equals the velocity of sound in fluid flowing through saiddevice, and 1 equals the frequency of impacts deliverable by saiddevice, and a spring on said valve to hold said valve open and to permitsaid valve to close in response to a predetermined rate of fluid flowthrough said inner tube to effect interruptions in said fluid flow, saidfluid flow interruptions effecting sudden downward movement of theassembly comprising said inner tube, said body member, said valve, andsaid bit connecting member.

References Cited in the file of this patent UNITED STATES PATENTS842,049 Wolski Jan. 22, 1907 1,330,736 Church Feb. 10, 1920 2,325,264Merten July 27, 1943 2,359,147 Merten Sept. 26, 1944 2,828,944 Udry Apr.1, 1958 2,836,395 Bielstein May 27, 1958 2,851,251 Mori Sept. 9, 19582,859,733 Bassinger et al Nov. 11, 1958 2,893,692 Marx July 7, 19592,903,240 Mathewson et al Sept. 8, 1959 2,905,439 Martini Sept. 22, 1959

1. IN A FLUID-ACTUATED PERCUSSION DRILLING DEVICE THE COMBINATION WHICHCOMPRISES AN OUTER TUBE, AN INNER TUBE CONCENTRICALLY POSITIONED WITHINAND SPACED APART FROM SAID OUTER TUBE, SAID INNER TUBE BEING OPEN AT THEUPPER END THEREOF INTO SAID OUTER TUBE, A VALVE AT THE LOWER END OF SAIDINNER TUBE, SPRING MEANS ON SAID VALVE FOR HOLDING SAID VALVE OPEN UNTILFLUID FLOW THROUGH SAID INNER TUBE EXCEEDS A PREDETERMINED RATE, ANDBODY MEANS SLIDABLY SECURED WITHIN SAID OUTER TUBE FOR SUPPORTING SAIDINNER TUBE AND VALVE, SAID BODY MEANS BEING PROVIDED WITH AT LEAST ONEFLUID FLOW PASSAGE THERETHROUGH IN COMMUNICA-